Izvestiya vuzov. Yadernaya Energetika

The peer-reviewed scientific and technology journal. ISSN: 0204-3327

On the control of coolant parameters in long service life installations

3/19/2020 2020 - #01 Chemistry, physics and technology of reactor coolants

Cherednichenko Yu.G. Levin O.E. 

DOI: https://doi.org/10.26583/npe.2020.1.09

UDC: 621.039.52

Control and maintenance within the preset limits of impurities of oxygen, iron and other elements are vitally needed during reaching by the facilities with heavy coolants and extended time of operation their operational regimes and during their operation. Concentrations of these impurities determine the main mechanism and kinetics of corrosion processes in structural materials. With time, concentrations of elements constituting part of structural materials increase in the coolant. They interact with dissolved oxygen, thus resulting in the formation of oxygen suspensions in the coolant impacting the coolant oxidation potential. Sensors based on solid oxygen-ion electrolytes are conventionally used in order to control oxygen in molten metal coolant. Analysis of methodological aspects of control of oxygen dissolved in non-isothermal circulation loops with metal coolants using such sensors is reported in the present paper. It was demonstrated that in the presence of dissolved loop wall materials and suspensions of their different oxides in the coolant implementation of control on the basis of values of oxygen activities and concentrations calculated for pure coolant is not justifiable in general terms.

Experimental distributions within the loop of oxidation potentials depending on the coolant temperature obtained in the process of long-term testing of wall material samples in molten lead in two circulation test facilities SM2-M and TsU1-M differing from each other by the principal methods applied for maintaining the preset modes as pertains to oxygen impurities are given in the present paper.

Operating mode was maintained in the SM2-M test facility by periodically suppling oxygen to the coolant surface in the pump tank, and that in the TsU1-M test facility was achieved by ejecting hydrogen directly into the loop. Within the low-temperature region the experimental values of oxidation potential in both test facilities were lower than those calculated for pure lead; this results in the difference in the oxygen concentrations calculated for pure coolant by up to two or more times for the loop sections with Tmin and Tmax. In other words, evident absence of constant oxygen concentration in the loop was observed. Besides the above the paper presents the variation of oxidation potential in the TsU1-M test facility during hydrogen ejection into the coolant in the course of its deoxidation. In this case, the oxidation potential in the loop varies in a complicated way, and raising the level of oxygen concentration does not make any sense at all.

The conclusion is that in long service life facilities oxygen parameters of the coolant must be controlled not by the oxygen activity or concentration values, but by the value of the oxidation potential in the area with maximum temperature. For obtaining the correct values of the oxidation potential, measurements should be carried out in the steady-state temperature conditions for the entire facility.

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control oxygen heavy coolant circulation loop oxygen!ion electrolyte oxidation potential